This invention relates generally to semiconductors, and more specifically to methods and apparatus for making anisotropic electrical interconnects.
Anisotropic electrical interconnects are known in the art. U.S. Pat. No. 6,194,492 B1 discloses an anisotropic conductive film which exhibits a conductivity in the thickness direction thereof by pressurizing the film in the thickness direction, the film including: an adhesive; and conductive particles dispersed in the adhesive; wherein the adhesive is a thermosetting or photosetting adhesive containing as a main component at least one kind selected from a group consisting of (a) a polymer obtained by acetalation of a polyvinyl alcohol, (b) a compound containing an allyl group, (c) a monomer containing an acryloxy group or methacryloxy group, and (d) a polymer obtained by polymerization of one or more selected from a group consisting of an acrylic monomer and a methacrylic monomer.
U.S. Pat. No. 5,932,339 discloses an anisotropically electricity-conductive film obtainable by dispersing in an adhesive agent electrically conductive particles, the adhesive agent being a curable adhesive agent comprising as a major component at least one polymer selected from the group consisting of an ethylene-vinyl acetate copolymer; a copolymer of ethylene, vinyl acetate and an acrylate and/or methacrylate monomer; a copolymer of ethylene, vinyl acetate and maleic acid and/or maleic anhydride; a copolymer of ethylene, an acrylate and/or methacrylate monomer and maleic acid and/or maleic anhydride; and an ionomer resin wherein molecules of an ethylene-methacrylic acid copolymer are linked with each other through a metal ion.
U.S. Pat. No. 5,865,703 discloses an anisotropic, electrically conductive adhesive film including insulating adhesive, electrically conductive particles dispersed in the electrically insulating adhesive, and transparent, spherical glass particles dispersed in the insulating adhesive.
U.S. Pat. No. 5,162,087 discloses an anisotropic conductive adhesive composition comprising an insulating adhesive component and particles dispersed in said insulating adhesive component, said anisotropic conductive adhesive composition being characterized in that said insulating adhesive component comprises a copolymer of acrylic ester having an alkyl group of 1-4 carbon atoms and a maleimide derivative, 5 to 60 parts by weight, based on 100 parts by weight of the copolymer, of a thermosetting resin, and 0.05 to 5.0 parts by weight, based on 100 parts by weight of the copolymer, of a coupling agent, and said particles are metallic-layer containing particles comprising a core made of resin, a metallic layer covering said core and a resin layer formed from finely divided resin fixed by the dry blending method on the surface of said metallic layer.
U.S. Pat. No. 4,740,657 discloses an adhesive composition or film capable of exhibiting anisotropic-electroconductivity comprising electroconductive particles comprising polymeric core materials coated with thin metal layers, and electrically insulating adhesive component.
U.S. Pat. No. 5,965,064 discloses an anisotropically electroconductive adhesive to be used for establishing electric connection between terminals of, for example, an IC chip and of a circuit pattern, which adhesive comprises an electrically insulating adhesive matrix and electroconductive particles comprise at least two electroconductive particulate products of different average particle sizes and wherein each particle of both the particulate products is coated with an electrically insulating resin insoluble in the insulating adhesive matrix.
U.S. Pat. No. 5,302,456 discloses an anisotropic conductive material including micro-capsules dispersed in a bonding resin. The micro-capsules contain, as a filler material, a conductor and a polymerization initiator, a curing agent or a curing promotor. A wall member encapsulating the filler material is formed of a thermoplastic or thermosetting insulative resin. Therefore, if the micro-capsules in the anisotropic conductive material are broken or destroyed by pressure or both of pressure and heat, electrical connection can be established between electrode pads and electrode terminals of a wiring substrate through the conductors contained in the micro-capsules. Simultaneously, the polymerization initiator, the curing agent or the curing promotor flows out, so that the insulative bonding resin is solidified.
The above prior art typically achieves the anisotropic effect by controlling filler loading. In other words, to obtain an anisotropic interconnect the adhesive must use few particles. However, these prior art methods still have serious leakage problems if the filler loading is too high or too uneven. The filler loading is hard to control especially if the filler responds to gravity or magnetic fields.